We do too in BrE, what I wrote was German (as in Sauerkraut). I confess I was using a table of ser/estar differences from a Spanish grammar book written in German. (That is why one or two of the verbs don't really count, but they were in the list because it makes a difference when translated into German.)

There are some words in German and English which have almost identical pronunciation (like sour/sauer) and being a little dyslexic, I often confuse the two languages.

It reminds of an observation I have made. If a woman tells a man "You look handsome today" the man says "thank you". If a man tells a woman "You look beautiful today" the woman says "What do I normally look like?".

I've always taken it as the difference in the ways that the sexes hear a statement, not in any way a comment on the nature of the English phrase. Most men figure out to omit the word "today", as it can accidentally turn an intended compliment into an insult.

I would like to know from a native Spanish speaking woman how the phrase "estas guapa" would be interpreted. Would you take it as a backhanded insult, or as a compliment.

It seems to me that if one knows that a woman has intentionally dressed up for some reason, then "estás guapa" would suggest that one has noticed and appreciated her effort. Tone of voice and expression undoubtedly help, too.

It seems as if "estás guapa" would be the correct compliment for a coworker. An added especialmente wouldn't hurt if it is your wife or girlfriend.

There is a decent Wikipedia article that states:The Spanish verb "ser" is etymologically related to the English words "essence" and "is", and estar with "state", "status", "standing", "stance" and "stay".